Hutchison Algebra I Burr Unit 8: Introduction to Quadratic Functions and Their Graphs *If you do have access to Google Classroom, please visit our class page and access the instructions and videos that accompany the lessons listed below. They appear on the Classwork tab under the materials for Weeks 3, 4, 5 and 6 and will probably answer many of your questions! There will be alternative and additional activities and practice available through Google Classroom and our Class Meetings. This Unit 8 Packet contains 6 lessons and some additional practice:

o 8-1 Exploring Quadratic Graphs

o 8-2 Quadratic Functions Part 1

o 8-2 Quadratic Functions Part 2 Examples & Practice

o 8-3 Finding x-Intercepts Part 1 Examples & Practice (*connects factoring to graphs and falling bodies!)

o 8-4 Vertex Form and Transformations Part 1 Examples & Practice

o 8-4 Vertex Form and Transformations Part 2 Examples & Practice In class, we might work through this in about 2 ½ weeks, but it may be more like 3-4 weeks of material if you are sticking to a goal of spending 30-45 minutes focused on your algebra 4-5 times each week (a goal that I strongly support). I’d suggest starting reading and working through the examples and practice on your own and then consulting the Completed Notes pages when a question arises. The solution/keys are provided so that you can have immediate feedback and identify what you already know and what you still need to learn more about. Use the keys to teach you and help you revise your work. Email me anytime with questions! When you sit down to work on this unit, clear a workspace, politely tell others you are unavailable for the next 45 minutes, set your timer, and focus in for some careful study. Stop and reevaluate when the timer goes off. The material is mostly sequential, but you COULD do the 8-2 Lessons AFTER 8-3 IF you’re like me and like factoring and modeling falling objects! Please email me each week to update me on your progress and let me know what else I may be able to do to help you learn! I would like to give you the opportunity to make up any missing tests from 3rd Quarter and to improve on topics that you may not have mastered yet! Please email me so we can make a plan! I also would love to hear about your recent calamities, conundrums, and adventures, school-related or not! Stay curious and creative, safe and sane, active and adventurous! And please keep in touch!!!! Erika G. Burr erika.burr@k12northstar.org +1 (907) 978-4481

8-1 Exploring Quadratic Graphs

• The graph of a quadratic function y = ax2 + bx + c is a U-shaped curve called aparabola.

• The highest or lowest point of the parabola is called the vertex.

Example 1: Identify the vertex of each graph. Tell whether it is a maximum or a minimum.

a) b)

Example 2: Make a table of values and graph each function. Find the vertex. Is the vertexa maximum or a minimum? Can you tell (without graphing) if your vertex is going to be amaximum or a minimum?

a) y = x2 b) y =12x

2 c) y = �2x2

1

Example 3: Without graphing, order the quadratic functions from widest to narrowest:

y = �4x2, y = 14x2, y = x2

Example 4: Graph the following functions. Compare the graphs.

a) y = x2 b) y = x2 � 4

Example 5: Graph the following functions. Compare the graphs.

a) y = 2x2 b) y = 2x2 + 3

8-2 Quadratic Functions (Part # 1)

• The vertex is the highest or lowest point on the graph.

• The axis of symmetry is the vertical line that splits the parabola down the middle.

Example 1: Find the vertex and the axis of symmetry for the following graphs.

a) b)

Vertex Formula: The graph of y = ax2 + bx + c has the line x = � b2a as its axis ofsymmetry. The x-coordinate of the vertex is x = � b2a . You can find the y by plugging x intoyour equation.

Example 2: Find the vertex and the axis of symmetry for the following functions.

a) y = 2x2 + 4x b) y = �x2 + 4x� 5

Up/ Down Test The graph of y = ax2 + bx + c opens upwards if a isand opens downward if a is .

Example 3: Determine whether the following functions open upward or downward.

a) y = x2 + 3x+ 4 b) y = �3x2 + 5x c) y = 2x� x2 + 6

1

Steps to Graph y = ax2 + bx+ c

• Find the vertex and the axis of symmetry. Sketch these in.

• Find the x-intercept by plugging in 0 for y.

• Find the y-intercept by plugging in 0 for x.

• Reflect your points across the axis of symmetry and connect your dots with a smoothU-shaped (not V-shaped) curve.

Example 4: Graph f(x) = x2 � 2x� 8

Example 5: Graph y = �x2 + 2x+ 3

2

Example 6: Graph y = 2x2 � 8x

Example 7: Suppose a particular “star” is projected from a firework at a starting height of520 feet with an initial upward velocity of 72 ft/sec. The equation

h = �16t2 + 72t+ 520

gives the star’s height h in feet at time t in seconds.

a) How long will it take for the star to reach

its maximum height?

b) What is the maximum height?

Practice:

8-2 Quadratic Functions (Part # 2)

• The axis of symmetry is the vertical line x = � b2a . The axis of symmetry divides theparabola in two equal halves.

• The vertex is the point (x, y) where x = � b2a . We then use this x�value in the equationto find y�value of the vertex. The vertex is the highest or lowest point on the curve.

Example 1: Find the equation of the axis of symmetry and the coordinates of the vertex.Does the parabola open up or down? Is the vertex a minimum or a maximum?

a) y = x2 + 14x� 9 b) y = �4x2 + 24x+ 6

Example 2: Find the equation of the axis of symmetry and the coordinates of the vertex.Does the parabola open up or down? Is the vertex a minimum or a maximum?

a) y = 16x� 2x2 b) y = 5x2 � 3

1

Steps for Graphing y = ax2 + bx+ c

1. Find the vertex and axis of symmetry. You use to find x and to find yyou .

2. Find the x-intercepts. Do this by plugging in .

3. Find the y-intercepts. Do this by plugging in .

4. Reflect any points, connect the dots.

Example 3: Graph y = x2 � 6x+ 5

Example 4: Graph y = �x2 + 4x� 3

2

Example 5: Graph the following quadratic functions.

a) y = 4x2 + 8x b) y = �2x2 + 3

Example 6: The total profit made by an engineering firm is given by the equation

p = �x2 + 24x+ 5000

where x is the number of clients the firm has and p is the profit. Find the maximum profit madeby the company.

Practice: 8-2 Quadratic Functions Worksheet

Practice: 8-2 Quadratic Functions Worksheet

Find the equation of the axis of symmetry and the coordinates of the vertex.

1. y = x2 � 10x+ 2

2. y = x2 + 12x� 9

3. y = �x2 + 2x+ 1

4. y = 3x2 + 3

5. y = 16x� 4x2

6. y = 0.5x2 + 4x� 2

7. y = �1.5x2 + 6x

Graph each function. Label the axis of symmetry and the vertex.

8. y = x2 � 6x+ 5

9. y = x2 + 4x+ 3

10. y = �x2 � 4x� 4

11. y = x2 � 2x� 8

12. y = 4x2 + 8x

13. y = 2x2 + 4

14. You and a friend are hiking in the mountains. You want to climb a ledge that is 20 feethigh. The height of the grappling hook you throw is given by the function

h = �16t2 + 32t+ 5.

What is the maximum height of the grappling hook? Can you throw it high enough toreach the ledge?

15. You are trying to dunk a basketball. You need to jump 2.5 feet in the air to dunk the ball.The height of your feet above the ground is given by the function

h = �16t2 + 12t.

What is the maximum height of your feet above the ground? Will you be able to dunk thebasketball?

4

Name:

1

8-3 Finding x�Intercepts of Quadratic Functions (Part # 1)

• The x�intercepts of a parabola are the points where the graph intersects with thex�axis. Equivalently, the x�intercepts are the points on the graph where y = 0.

• A parabola can have , , or x�intercepts.

Example 1: Identify and label the x�intercepts of each graph.

a)

b) c)

Example 2: Suppose that you multiply two numbers and the result is zero. What can wesay for sure about the numbers you multiplied?

Zero Product Property If the product of two (or more) numbers is equal to zero, thenone of the numbers must be zero.

Example 3: We can use the Zero Product Property to find the x�intercepts of the graph ofa polynomial function. We do this by substituting y = 0 and factoring the expression! Find thex�intercepts of each parabola.

a) y = 2x2 + 4x b) y = x2 � 4x+ 5

1

Steps to find x�intercepts of factorable quadratic functions:

• Write the equation of the function in standard form: y = ax2 + bx+ c

• Substitute y = 0.

• Factor the expression ax2 + bx+ c.

• Set the resulting factors equal to zero and solve for x.

Example 3: Find the x�intercepts of each function.

a) y = x2 + 4x+ 4 b) y = �3x2 + 6x c) y = 2x2 + x� 6

Example 4: Graph f(x) = x2 � 2x� 8

Example 5: Suppose model rocket is launched from a platform 128 feet off the ground withan initial upward velocity of 64 ft/sec. The equation h = �16t2 + 64t + 128 gives the rocket’sheight h in feet at time t in seconds. When will the rocket hit the ground?

Practice: Finding x�Intercepts Worksheet

Practice: 8-3 Finding x�Intercepts Worksheet #1

Find the x�intercepts of each parabola.

1. y = x2 � 6x+ 9

2. y = x2 + x� 9

3. y = �x2 + 2x� 1

4. y = 3x2 � 3

5. y = 16x� 4x2

6. y = 4x2 + 11x+ 6

7. y = x2 + 6x

Graph each function. Label the axis of symmetry, the x�intercepts, and the vertex.

8. y = x2 � 6x+ 5

9. y = x2 + 4x+ 3

10. y = �x2 � 4x� 4

11. y = x2 � 2x� 8

12. y = 4x2 + 8x

13. y = x2 � 4

14. You and a friend are hiking in the mountains. You want to climb a ledge that is 20 feethigh. The height of the grappling hook you throw is given by the function

h = �16t2 + 38t+ 5.

We already know you can throw it high enough, but what if you miss? After how manyseconds will the hook land back where you are standing?

3

Name:

1

8-4 Vertex Form and Transformations (Part 1)Example 0: Graph the functions. Recall that x = �b2a gives the x�coordinate of the vertex.

a) y = x2 � 6x+ 8b) f(x) = �2x2 � 4x� 2

Example 1: Make a table to graph the following functions.

a) y = (x� 3)2 � 1 b) f(x) = �2(x+ 1)2

Vertex Form: The vertex form of a quadratic function is given by

f(x) = a(x� h)2 + k

where (h, k) is the vertex of the parabola and a describes the orientation and stretch orcompression compared to the graph of y = x2.

1

Example 2: Identify the vertex of each parabola from the equation. Then match each equa-tion with its graph.

a) f(x) = (x+ 2)2 � 5 b) g(x) = 2(x� 1)2 + 3 c) h(x) = �x2 + 4

Example 3: Sketch the graph of each parabola. Show at least 5 precise points.

a) y = x2 b) f(x) = (x+ 3)2 c) f(x) = (x� 4)2 � 1

Practice: 8-4 Vertex Form Worksheet # 1

8-4 Vertex Form Worksheet # 1

Identify the vertex of each parabola fromthe equation. Then match each equation withits graph.

1. f(x) = x2 � 4

2. y = 3(x+ 2)2 + 1

3. g(x) = �x2 + 9

4. h(x) = (x� 3)2 � 2

5. y = (x� 1)2 � 3

•

•

•

•

•

•

•

•

6. Sketch the graph of the function. Showat least 5 precise points on the parabola.

p(x) = (x+ 5)2 � 1

3

8-4 Vertex Form and Transformations (Part 2)Example 1: Graph the following functions. First identify the vertex, then find points nearby.

Include at least 5 precise points on the parabola.

a) y = (x+ 4)2 � 2 b) f(x) = 2x2 � 9

Vertex Form: The vertex form of a quadratic function is given by

f(x) = a(x� h)2 + k

where (h, k) is the vertex of the parabola and a describes the orientation and stretch orcompression compared to the graph of y = x2.

Example 2: Write the equation for each parabola in vertex form.

a) b) c)

1

Reflection, Compression, and Stretch: Given f(x) = a(x� h)2 + k,

• If a > 0, the parabola .

• If a < 0, the parabola .

• If |a| > 1, the parabola compared to the graph of y = x2.

• If |a| < 1, the parabola compared to the graph of y = x2.

Example 3: Describe the transformations needed to obtain g(x) from the graph of y = x2.

a) g(x) = 2x2 � 3

b) g(x) = 2(x� 3)2 � 1

c) g(x) = �12x2

d) g(x) = (x+ 5)2

e) g(x) = (x+ 1)2 � 3

f) g(x) = �2(x� 4)2 � 7

Example 4: Sketch the graph of each parabola using transformations. Show at least 5 precisepoints.

a) y = �x2 + 4 b) f(x) = 2(x+ 3)2 c) f(x) = 12(x� 4)2 � 1

Practice: 8-4 Vertex Form Worksheet # 2

8-4 Vertex Form Worksheet # 2

Write the equation for each parabola in ver-tex form.

1.

2.

3.

4.

5.

Describe the transformations needed to ob-tain g(x) from the graph of y = x2. It is fine touse the grapher at desmos.com to check!

6. g(x) = x2 + 9

7. g(x) = 3(x+ 2)2 + 1

8. g(x) = �x2 + 1

9. g(x) = �2(x� 3)2 � 2

10. g(x) = 12(x� 1)2 � 3

Sketch the graph of each parabola us-ing transformations. Show at least 5 precisepoints.

11. f(x) = (x+ 5)2 � 1

12. h(x) = 2(x� 3)2 � 4

3